In the past 3-5 months, I have noticed clicking on the back of my knees when I begin my stretching or kicking. When it comes to kicking, this usually only happens if I haven't stretched or warmed up properly, on the leg which I am using as support, NOT the one I am kicking with. As for stretching, I've just had it happen towards one of my final exercises of my stretching routines so I'm sure I was warmed up. Should I be concerned? It's not the type of click that you get from bones click, such as when you wake up and your elbows click or when you crack your knuckles. It feels different, but there's no pain, perhaps some discomfort but I believe it's psychological. How do I proceed and how do I stop it? Is it serious?